A radio LAN system is one of radio packet communication systems that have recently been standardized as systems for implementing high-speed data transmission by radio. In this radio LAN system, a plurality of radio stations form one radio link and share one channel by CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance). In the radio LAN system, if adjacent radio links use the same channel, the throughput decreases due to cochannel interference. Conventionally, in the radio LAN system, as a technique of preventing interference from radio waves forming different radio links, the technique disclosed in Ishi et al., “Proposal of Packet DCA for Radio LAN” (Proceedings of 1996 IEICE Society Conference B-652) (reference 1) is available.
The technique disclosed in this reference 1 is characterized as follows. To prevent interference between one radio station belonging to a given radio link and the other radio station belonging to another radio link in a single radio communication system, each radio station transmits/receives a control packet upon forming a new radio link. When a given radio station receives a control packet from another radio station, the radio station determines that the corresponding channel is used by the other radio station in the same radio communication system, and selects a channel for which a control packet from another radio station is not received, thereby preventing interference with other radio stations in the same radio communication system.
In the radio LAN system, in communication between radio stations belonging to different radio links, when the two radio links are connected to a single wire network via base stations and the like, the radio station on the transmitting side transmits a packet to a base station connected to the radio link to which the self-station belongs, and the base station transfers the packet to a base station connected to the radio link to which the radio station on the receiving side belongs via the wire network. The base station connected to the radio link to which the radio station on the receiving side belongs transmits the packet to the radio station on the receiving side, thereby implementing communication.
In the conventional systems, no consideration is given to communication between radio links using different channels. For this reason, in a radio packet communication system like the radio LAN system described above, communication cannot be efficiently performed.
According to the channel selection method described in reference 1 and the like, different channels are used for adjacent radio links. When two radio stations belonging to the respective radio channels are to communicate with each other, they cannot directly communicate with each other, because they use different channels, regardless of whether they are located at a distance from each other within which direction communication is allowed.
In addition, as described above, although communication can be performed via a wire network in some cases, when, for example, two radio stations belong to radio links to which no base stations are connected or base stations, if any, are connected to different wire networks, the two radio stations cannot communicate with each other. In some cases, therefore, in a radio packet communication system like the radio LAN system described above, even radio stations that are otherwise capable of direction communication cannot communicate with other by using the conventional radio communication apparatus.
In communication via a wire network, as described above, since communication between radio stations and base stations is performed via two radio links, the radio channel usage is twice that for direct communication. Therefore, when radio stations belonging to different radio links communicate with each other, the number of used channels doubles as compared with the case of direct communication.